Billy Horschel acknowledges the cheers on the 17th hole on his way to a second-round 67. / Michael Madrid, USA TODAY Sports

by USA TODAY Sports, USA TODAY

by USA TODAY Sports, USA TODAY

ARDMORE, Pa. - Billy Horschel made three birdies and hit 18 greens in regulation on Friday. That's a pretty good recipe for success.

Phil Mickelson made only one birdie, but it came after the horn sounded and as the sun set. That's a pretty good way to close out a round and keep yourself at the top of the leaderboard.

Mickelson (72) and and Horschel (67) share the clubhouse lead in the incomplete second round of the 113th U.S. Open at Merion Golf Club.

They are at 1-under 139 overall.

Mickelson was alone in front after the first round, but struggled on the greens throughout the day Friday before burying a long birdie putt on 18.

"I wasn't expecting birdie there," Mickelson said of his putt at the last hole. "It's a very difficult hole.

"I got shut out today. I played really well. Even though I shot 2 over, it was the birdie opportunities that I didn't capitalize on. Had I made one on 2 or that birdie on 8 or 9 or 11, I would have changed kind of the momentum of the round. I played well today even though I didn't feel the score was what I thought it should be."

Horschel missed the cut in his only previous U.S. Open, 2006, but recently won for the first time on the PGA Tour at the Zurich Classic.

"I've acquired some patience, not as much as I wish I had," the 26-year-old Horschel said. "The older I get, the more mature I get on the golf course, the more understanding that if I do have a bad stretch of holes, it's not that I don't hit the panic button, I just don't press right away."

Three of the game's top players still chasing that first major championship are one shot back and in the hunt. Luke Donald (72), Justin Rose (69) and Steve Stricker (69) were in the clubhouse at even par.

Rose managed to get his round finished after the horn had sounded, meaning he won't have to be back at the course early Saturday.

"When you're up at the top end of the leaderboard, you know you're going to have a late tee time," he said. "It's hard to start at 7:30 in the morning and wait until 1 or 2 to play. That lying in in the morning is going to feel very good."

Many of the late-afternoon tee times did not finish Friday night - 68 players were still on the course when play was suspended - thanks to Thursday's two weather delays, and the second round will be completed Saturday morning.

Amateur Cheng-Tsung Pan of Taiwan, a junior at the University of Wasthington, and Ian Poulter of England were both at even par with holes to play. Pan was through nine holes, Poulter, a Ryder Cup hero with limited major success, was through 14 holes.

John Senden (71) of Australia and Nicolas Colsaerts (72) of Belgium were at 1 over.

The host course, playing only 6,996 yards, was brutal on Friday as most every player in the field found himself headed in reverse.

The scoring average for the second round stands at 75.17, more than five strokes over par.

"It's tough. There's no letup. It doesn't matter how long it is," said Masters champion Adam Scott, who shot a second-round 75, leaving him at 7 over par. "You've still got to hit the fairway. The rough is really penal."

Scott played in the marquee grouping with Tiger Woods and Rory McIlroy, who were at 3 over after each shot 70 in the second round.

Woods then dropped his left hand off the club and shook his wrist while putting his tee shot wide of the fairway at No. 8, just as he had done several times on Thursday. The left arm clearly bothered him again on the next shot, which he put in the rough near the green. He saved par on the hole, helping him stay in contention if he can stay healthy.

"It's hard with the wind and the pin locations," Woods said. "They're really tough. ... We didn't think they were going to be as severe as they are."

Woods was tight-lipped about his elbow, saying only that it first bothered him at the Players Championship five weeks ago. Asked what he felt, he answered: "Pain."

Four-time major champion Ernie Els was at 3 over.

The top 60 and ties will play Rounds 3 and 4; the projected cut was at 8 over par.

Mickelson has finished second at the U.S. Open a record five times. He's in the mix again.

"I think it's fun having a chance heading into the weekend," he said. "The way I have control off the tee and as good as the putter is, even though it didn't show today, I'm very excited about the opportunity this weekend."